The invention relates to a method for fertilizing cultivated plants in order to optimize the quantity and quality of the yield by optimizing the quantity of nitrogen fertilization through the utilization of a bio-indicator of the plant. The invention is associated with the planning and implementation of an optimal fertilization method in plant cultivation.
FI patent publication 102 135 discloses a fertilization method wherein there is spread in connection with the planting of the seed an initial fertilizer amount, which is 50-75% of the fertilizer amount corresponding to the maximum yield. During the growing season, a yield prediction is calculated by heat summation, and the need for additional fertilization is calculated by means of this yield prediction. The object of this method is to achieve a maximal yield in terms of quantity. The said method is primarily a corrective method and, for example, it does not optimize the efficiency of nutrients.
Nowadays the amount of nitrogen fertilization is calculated according to the plant species and plant variety, the target yield, the properties of the soil, such as the content of organic matter in the soil, and the preceding plant species grown in the area (pioneering plant). xe2x80x98Areaxe2x80x99 may here denote, according to the situation, a small area, e.g. 1 m2, or a large area, e.g. 15 hectares.
In practice, the fertilizer is spread on the surface, is placed in the soil either between rows of planted seeds or between rows of seedlings, or is applied directly to the actual row of seeds or is sprayed in liquid form onto the leaves. Depending on the plant species cultivated or on the place of cultivation (agroecologic area), the fertilizer is applied either all at once or, alternatively, a portion at the time of planting and a portion according to the need to be determined during the growing season.
For the monitoring of balanced nitrogen nutrition, many laboratories are specialized in the analysis of plant and soil samples and in issuing nitrogen fertilization recommendations on the basis thereof. The making of nitrogen fertilization recommendations during the growing season is often based on the so-called DRIS method or on comparison with other known optimum curves (Anon. 1990, Beaufils 1973, Siman 1974). As a procedure, the above-mentioned practice is slow, since sending samples to the laboratory, analyzing the results, sending them back to the grower, and making the fertilizing decision on the farm take a great deal of time, during which much can change in the cultivated field.
Attempts have been made to eliminate the time problem by developing meters with which it is possible to measure the nitrogen status and nitrogen concentrations of the plant stand directly in the field. The nitrogen status of plants has been measured with color reaction papers (ammonium and nitrate nitrogen). With various portable laboratory kits it is possible to measure the nitrogen status of plants and the soil in the field under cultivation (Pulkkinen 1999). For example, portable meters have been developed for measuring the greenness, i.e. chlorophyll, of a plant stand (Watanabe et al. 1980) and the nitrate concentration in the cell sap (Scaife and Stevens 1984). These described methods do not, however, make possible a very precise, patch-specific monitoring of the nitrogen status in several parts of a field. In other words, even these methods are too laborious for patch-specific measuring of large sectors.
The latest systems include sensors installable in tractors, and growth quantity and nitrogen analyses made from aerial photographs or satellite photographs. Specifically the technology associated with the precision farming concept, which is made up of a localization system (GIS and GPS technology) and of sensors installed in production equipment such as a combine, a tractor, etc. (Wollring et al. 1998) and of yield quality meters (protein sensors, http://www.casecorp.com/agricultural), is now enabling data to be collected from very small sub-areas of a field. In practice, sub-areas of approximately 10 metersxc3x9710 meters have been handled. In addition, software has been developed for processing the patch-specific data (Grandzinski et al. 1998).
The problem in the planning of the total nitrogen amount and/or the supplementary or divided nitrogen fertilization technique during the growing season in precision farming today lies in that the nitrogen amounts are calculated for the real yield quantity on the basis of yield mapping or for a new target yield, if the productivity of the soil has changed for one reason or another. However, it is not possible to show in advance that the projected nitrogen amount would in any way be optimal under the prevailing growth conditions. In other words, the grower should be able to identify patch-specifically the yield potential for the time concerned. So far, there have been no other methods for identifying the yield potential in precision farming than to collect patch-specific yield date over several years, in which case the best possible yield level can be found through yield mapping of several years when a certain fertilizer input is used.
Because of the above-mentioned problem, for example in nitrogen fertilizer planning with the help of sensors or false-color photos during the growing season, the target is rather a uniform greenness or uniform formation of leaf area. In other words, the target is rather to homogenize the greenness of the plant stand and the formation of leaf area, and not to adapt the fertilization to the real varying yield formation potential in different patches of the field. Since it is, however, a known fact that the productivity of different patches in a field varies, and thus the total need for nitrogen fertilization also changes as productivity changes, the above-mentioned method for distributing nitrogen fertilizer during the growing season does not necessarily improve the efficiency of nitrogen fertilization and the yield in the expected manner.
Another problem is that the success of a nitrogen fertilization program implemented by the current technology cannot with certainty be verified reliably in connection with harvesting. Success could be observed experimentally by organizing in the field an experiment of increasing nitrogen fertilizer amounts (so-called fertilization windows, Anon 1992), but even this procedure is not in practice successful in precision farming. Owing to intra-sector variation, there should be an almost innumerable number of tests in different parts of the field.
The object of the invention is to provide a fertilization method by which the quantity and quality of the yield can be optimized and the nutrient load can be minimized, and by which the variations of growth among different sub-areas of the cultivated area are taken into account.
According to the invention, there is thus provided a method for fertilizing cultivated plants so that the quantity and quality of the yield are optimized with the help of a bio-indicator, in which method, before the establishment of a plant stand, the following steps are taken:
the area to be cultivated is divided into sub-areas;
the potential yield is determined in each sub-area on the basis of a bio-indicator;
the optimal bio-indicator level aimed at for the potential yield is selected; and
the nitrogen fertilization requirement for achieving the desired optimal bio-indicator level in the potential yield is determined,
and thereafter, in connection with the planting of the seed, nitrogen fertilizer is spread, and optionally after the planting nitrogen fertilizer is applied once or several times according to the said fertilizer requirement, the realization of the potential yield being monitored during the growing season in each sub-area by means of growth measurement, and on the basis of these measurements additional nitrogen fertilizer is applied, when needed, once or several times in order to reach the desired bio-indicator level.
According to the invention it is possible to use, for example, a fertilization method commonly used in Northern Europe, in which method most of the fertilizer is spread in connection with the planting of the seed and is supplemented with additional fertilizer according to need during the growing season. It is also possible to use the divided fertilization method prevalent in Central Europe, in which method fertilizer is spread in the field 2-7 times.
The bio-indicator used is a nitrogen-containing compound of the plant. If the cultivated plant is a grain, the said bio-indicator used is a protein. If the cultivated plant is, for example, sugar beet, the bio-indicator is an amino nitrogen (xcex1-amino nitrogen).
The measuring of the said bio-indicator can be performed, for example, by using a sensor technique, aerial photography, or satellite photography.
According to the invention, the quantity of the yield of the growing season or of the previous growing season or of previous growing seasons and the bio-indicator level of the yield in each sub-area are taken into account in the determination of the nitrogen fertilization requirement. In this case the procedure is preferably that, at the harvesting stage a yield map and a bio-indicator map, such as a protein map, are prepared, and these maps are then used in preparing the fertilization recommendations for the subsequent growing seasons.
The invention thus relates to an entity based on the utilization, in a novel manner, of bio-indicators such as the protein content of the cultivated plant, and additionally the yield prediction derived from the leaf area and/or phytomass or the actual yield, in the making of fertilization plans. The best possible yield, i.e. the potential yield level, can be determined with precision with the help of bio-indicators. Furthermore, it is possible to take into account the natural nitrogen available in the soil; this has so far been difficult to do patch-specifically in cultivation.
In the invention, the data measured from the plant stand, for example by sensor techniques (the radiation reflected by the plant stand is measured, for example, in wavelength ranges of 600 and 800 nm) or by using the false-color techniques of aerial or satellite photographs and other patch-specific (GIS/GPS technique) data regarding the soil (soil productivity) and the yield (yield and quality maps). The measurement data are utilized in real time by using mathematical models and bio-indicators of the plant stand, by means of which fertilization to be applied during the measuring or thereafter is controlled.
The inventive idea of the method is that, before the actual fertilization recommendations are made, the crop yield potential of the plant stand is identified on the basis of a bio-indicator. When a grain is concerned, the bio-indicator used for the overall planning of fertilization is the protein content realized in the crop (post-harvest evaluation) and, respectively, for specific fertilization during the growing season the bio-indicator used is the protein content being realized, forecastable with the help of models. If the optimal protein content typical of a grain species and grain variety has been realized/is being realized, the nitrogen fertilization is correctly planned for the production conditions of that time. Instead, if the protein content is clearly higher than the determined optimal level, the crop yield has been maximized and nitrogen fertilization can be reduced, unless a high protein level is especially interesting commercially and a desirable property in the crop. Respectively, if the protein content of the crop is lower than the determined critical limit value, the yield will increase when nitrogen fertilization is increased.